Using a patterned paper, cut 4.25" x 7". When finished, the white will be on the outside but to mail, I put them in a larger envelope. These are a great size to pass out in class or in person. Next is the scoring and on the long sides, score at 1/2". Turn your paper to score at 4 3/4" and 1 1/2"( in the video that I linked, she scored at 1" x 4.25").
Trim the 1/2" sides as in the above picture. Round the corners and glue the edges. In the above picture, both envelopes are shown and the one on the top is the adjusted (my measurement) and the bottom is the one from this video. http://www.wonderhowto.com/how-to-make-envelope-for-3-x-3-card-328444/